Technical Field
Embodiments of the invention relate generally to noise filtering in imaging systems. Particular embodiments relate to filtering gradient coil power amplifier noise in magnetic resonance imaging (MRI) systems.
Discussion of Art
Generally, the quality of images produced by an MRI system will be affected by the repeatability and fidelity of its electronic components. In particular, gradient subsystem power amplifiers strongly influence the fidelity with which a scan volume is voxellated (scanned in volume segments of equal size and common orientation). For example, power amplifier ripple or swerve can degrade a desired uniformity of voxel size and orientation.
Accordingly, MRI systems are provided with apparatus for correcting images in response to deviations in the performance of electronic components such as the gradient subsystem power amplifiers. One such apparatus is a ripple cancellation filter, which is provided to reduce switching noise produced at the gradient coil by pulse width modulating the gradient power supply. Typically, the ripple cancellation filter is a hidden component that becomes known to an end user only while trying to diagnose a source for narrowband noise (at about the pulse width modulation frequency of the gradient coil power amplifiers) in an expensive set of MR images. Determining whether a ripple cancellation filter is properly working has typically been an invasive exercise of opening up the filter box and using hand instruments to read component electrical parameters.
In view of the above, it is desirable to provide apparatus and methods for proactively and non-invasively assessing performance of a ripple cancellation filter within an MRI system. Such apparatus and methods might also be helpful toward real-time assessing performance of ripple cancellation filters in other types of electronic systems.